It is well understood that vessels or structures that in part reside below the surface of sea water or fresh water are subjected to various levels of fouling by marine (salt water) or aquatic (fresh water from lakes and rivers) organisms, respectively. Vessels such as boats, ships, or submarines require routine removal (cleaning) of fouling such as algae, weed, barnacles, mollusks, etc., in order to maintain the performance or even the function of the vessel. At the base of the fouling mechanism for vessels and structures residing in sea or fresh water are the biofilms formed on such structures that constitute the glue between marine or aquatic organisms and the actual structure. The biofilms form and the fouling-organisms attach to all subsurface structures and as a result the more diverse or intricate the structure (such as propellers, rudders, inlet and outlet ports, sonar housings, protective grills, etc.) the more difficult and costly to remove the biofilms and these organisms. Fouling is a major problem, leading to higher fuel consumption and consequently increased air pollution. It can also cause the spread of alien species that do not belong in the local marine environment. The type of paint or coatings applied to the vessel or structures also change the types of fouling. The economic impact of fouling is very high too. For example, in the US Navy the propeller cleaning is recommended up to six times a year and hull cleaning or grooming is recommended up to three times a year.
The fouling of platform structures below the water's surface such as pilings and beams creates an uneven water flow around the supporting features, which causes an uneven pressure distribution throughout the structure leading to material stresses and the potential for collapse of the platform. In conclusion a system that can perform a thorough grooming, meaning the removal of the biofilm(s) from structures and vessels, prevents the organisms from growing to a size that affects the vessel or structure's function or performance, which will require cleaning (removal of microorganisms and biofilms).
The cleaning or grooming of a marine (salt water) or aquatic (fresh water) vessel or structure (such as oil platforms) generally involves methods that use brushes, scrapers, other abrasive means to clean and very high pressure water sprays. Abrasive methods can be damaging to the welds and rivets of the water vessels or underwater structures compromising their mechanical integrity. Some of these methods require that the water vessel be dry-docked, which is a not only a large expense but a risk to the structure of the vessel each time it is removed from the water. Present cleaning or grooming methods are labor intensive and fall short of being thorough, leaving behind the biofilms, which represent the substrate and hold the nutrients that different salt water or fresh water organisms use for growth and anchor. Due to this drawback, the actual marine (salt water) or aquatic (fresh water) vessels or structures will need cleaning more often. These other methods also tend to remove one or more surface layers of coatings or paint protecting the vessel or platform structure, which can requires that it be recoated or repainted. When the cleaning or grooming is performed below water surface another drawback may occur due to the fact that removed coatings or paint from the ship can be toxic for the surrounding marine or aquatic life.
Patents US 2005/0199171, US 2012/0006244, US 2013/0298817 and US 2014/0230711 present different systems and methods that use brushes to clean ship hulls. These systems can be used without the necessity of dry docking the ship. These patent publications present support frames with articulated arms or movable chassis/frames that help the brushes to reach the actual area that needs to be cleaned. These systems are complicated, expensive, labor intensive and can be dangerous to divers. Furthermore, it is well known that the brushes also remove a significant amount of the anti-fouling paint (a third of the paint coating can be gone during cleaning or grooming process), which can significantly increase the cost of cleaning or grooming, due to the necessity of re-painting of the hull.
A robotically operated device that uses an ultrasonic transducer for cleaning of ships' hulls is presented in U.S. Pat. No. 4,890,567. This device was designed to be used during dry-dock cleaning of a ship and also can be used to spray paint on the hull after cleaning. The cavitation generated by the negative pressure of the ultrasound is thought to be the main mechanism that produces the hull cleaning. However, the ultrasound by its nature has a weak negative pressure (this pressure generates cavitational bubbles) and is immediately followed by the tensile (positive pressure), which collapse the cavitation bubbles before reaching their maximum size and thus full cleaning power. This is why this method is less effective, labor intensive and requires the dry-docking of the ship, which dramatically increases the cost.
High pressure water sprays systems for cleaning ship hulls (U.S. Pat. No. 6,595,152) or pile cleaning of submerged structures (U.S. Pat. No. 8,465,228) represent popular systems that are used for cleaning of marine (salt water) or aquatic (fresh water) vessels or structures. The disadvantage of these systems is the high operating pressures that can be dangerous for the divers and damaging to the actual structures that need to be cleaned. Not to mention that these systems require bulky installations and a lot of safety features to make them as safe as possible.
A “cavitation (negative pressure) jet” technology has been developed, such as described in U.S. Pat. No. 7,494,073, for use in cleaning surfaces underwater, with the added benefit of removing little to none of the coatings or paint layers, and therefore making the cleaning process of little to no contamination risk to the surrounding marine environment. However, this is a hand-held system by a diver that was designed for action on small surfaces (due to the nature of jet technology) and still requires a labor intensive operation to accomplish the desired results. Larger systems were created by Russians that are called “cavitators”. These systems rely only on hydrodynamic cavitation bubbles that collapse and send so-called localized “shock waves” towards the surface in need of cleaning. Due to high pressures used for the jets providing flowing liquid and gas that generate the cavitation, the cavitation bubbles do not have an optimum environment to develop to their full potential (high pressures from outside the bubbles prevent them to grow to their largest dimension, which translates in less energy put in the so-called “shock waves” produced during their collapse), which reduces significantly their efficiency. In other words, the smaller the pressure outside the cavitation bubbles (unpressurized liquid) the larger the bubbles will grow until the pressure inside the bubbles is higher than the pressure outside the bubbles, which will initiate their collapse capable of generating much more efficient high pressure jets.
All of the above alternatives for cleaning or grooming underwater structures or ship hulls rely on the support of a remotely operated “underwater” vehicle (ROV). The ROV is commercially fabricated for various purposes including underwater applications. These ROVs allow underwater navigation while being remotely controlled above water surface. Remote navigation is possible since ROVs contain onboard cameras and underwater lighting systems to transmit live images of the environment surrounding the ROV to the above surface station/control station. The ROVs are equipped with thrusters to propel the ROV through the water and contain wheels, traction grip tracks, or other traction means such as controlled suctioning or controlled magnetic attraction to move along a surface. There are particular commercial ROVs that can maintain direct contact with an underwater structure while traversing alongside it, even beyond vertical. These highly developed and capable ROVs require extensive technical expertise [refer to patents U.S. Pat. No. 8,886,112, US 2011/0083599, US 2013/0263770, US 2014/0076224 A1, US 2014/0076225 A1, and US 2014/0081504 A1] to support their unique capabilities, which is not in the scope of this invention.